Electronic components, such as integrated circuit chips, are commonly attached to a substrate (e.g., a printed circuit board (PCB) or printed circuit card (PCC)) with solder connections using a ball grid array (BGA), chip scale package (CSP), or direct chip attach (DCA) technique. Occasionally, an electronic component may be found to be defective, and will therefore have to be removed and replaced with a functional electronic component using a rework process. In a conventional rework process, the defective electronic component is removed by first heating the solder material, used to connect the component's solder connectors to corresponding contact pads on the substrate, to its melting, or "reflow" temperature. Then, the defective electronic component is pulled off the substrate and replaced.
In a conventional rework process, a stream of hot gas is typically directed toward the top of the electronic component. This method works well if the solder connections are only located around or near the periphery of the electronic component, or when there is a relatively large gap between the bottom of the electronic component and the substrate. Unfortunately, using currently available reflow methods, heat from the stream of hot gas is not effectively or evenly transmitted to solder connections located away from the periphery of the electronic component (e.g., near the center of the electronic component). This is especially problematic if the space between the electronic component and the substrate is small, thereby restricting the flow of hot gas from the periphery to the center of the electronic component.
Electronic components mounted on a substrate commonly require underfill to increase reliability, mechanical integrity, and to ensure adequate operational life. For example, an underfill material such as epoxy is commonly inserted between an electronic component and a substrate to cover the solder connections, thereby protecting the solder connections from corrosion causing fluids or gases, and mechanically strengthening the connection between the electronic component and the substrate. Further, the use of underfill reduces failure of the solder connections due to cycling stresses caused by differences in the coefficients of thermal expansion of the electronic component and the substrate. Thus, underfill provides a robust mechanical connection preventing damaging relative motion between the electronic component and the substrate.
Commonly, the underfilling is accomplished by depositing a bead of underfill material along one or more sides of the electronic component and allowing capillary action to pull the underfill material under the electronic component. Unfortunately, not only is the process relatively slow and may leave voids in the underfill, but also requires the underfill material to be very fluid in nature. Thus, restrictions are placed on the composition of the underfill material.